layout: Account for transform in scrollable overflow (#36138)

In the scrollable overflow calcutation, apply CSS transforms to boxes
and scrollable overflow of the descendant. Clip unreachable scrollable
overflow according to it's block start and inline start scrolling
direction. And, renamed `Fragment::scrolling_overflow` to
`Fragment::scrolling_overflow_for_parent` as it was calculating the
scrolling overflow contribution from a child.

Add several WPT tests, testing the transform interaction `rotate`,
`scale`, and `skew` with scrollable overflow. There are several WPT test
that are testing the interaction that not expected from current browsers
implementation according to the spec.

Testing: Existing and new WPT. 
Fixes: #36031

---------

Signed-off-by: stevennovaryo <steven.novaryo@gmail.com>

components/layout/fragment_tree/fragment.rs

@@ -170,17 +170,28 @@ impl Fragment {
         }
     }
 
-    pub fn scrolling_area(&self) -> PhysicalRect<Au> {
+    pub fn unclipped_scrolling_area(&self) -> PhysicalRect<Au> {
         match self {
             Fragment::Box(fragment) | Fragment::Float(fragment) => {
                 let fragment = fragment.borrow();
                 fragment.offset_by_containing_block(&fragment.scrollable_overflow())
             },
-            _ => self.scrollable_overflow(),
+            _ => self.scrollable_overflow_for_parent(),
         }
     }
 
-    pub fn scrollable_overflow(&self) -> PhysicalRect<Au> {
+    pub fn scrolling_area(&self) -> PhysicalRect<Au> {
+        match self {
+            Fragment::Box(fragment) | Fragment::Float(fragment) => {
+                let fragment = fragment.borrow();
+                fragment
+                    .offset_by_containing_block(&fragment.reachable_scrollable_overflow_region())
+            },
+            _ => self.scrollable_overflow_for_parent(),
+        }
+    }
+
+    pub fn scrollable_overflow_for_parent(&self) -> PhysicalRect<Au> {
         match self {
             Fragment::Box(fragment) | Fragment::Float(fragment) => {
                 fragment.borrow().scrollable_overflow_for_parent()